Computer wont boot! help! canot load dos! error message

hi experts im in desperate need for help.....everytime i turn on my computer i get a error 'cannot load dos! any key to retry"

this happenned after the people at trend micro sent me a utility thad made a chnage to the registry....after the change was made they told me to reboot and when i did that i started to get that error messsage and the computer wont boot at all !!....i did not make a backup of the registry cuz i trusted  trend micro and didnt thing that theirr registry change was going to mess up my computer,,...i dont even get to the menu where i can boot to safe mode or last know good configuration!!..the only menus i can get to is the setup menu and the boot emnu thats is a DELL DIMENSION 8250.....please help me.....!! i need this PC up and running it is very important............needles to say that the people at trend micro do not know how to fix this problem....
James HilloyaAsked:
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There are no operating systems for the PC.
Check your BIOS :
Is the harddisk ok ?
And the Boot order is ok ?

Boot on a floppy or your XP CD and let it run some screens to before you have to choose a partition to install to.
Hit F3 and reboot.

XP can have reenabled his OSLoader.

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Windows XP

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